Jet fuel manufacture



Feb. 22, 1966 Original Filed June 29. 1961 M. J. DEN HERDER ET AL 3,

JET FUEL MANUFACTURE 2 Sheets-Sheet 1 CATALYTICALLY CRACKED GAS OIL Flg. 1

Hydrogen Hydr ogen DISTILLATION V v Hydrogen FlRST FIRST FIRSTHYDROGENATION HYDROGENATION HYDROGENATION S 8 N S 8 N S 8 N CompoundsCompounds %T5'lil and H and H 2 SEPARATION SEPARATION SEPARATIONHydrogen ---0Hydrogen ---O Hydrogen l SECOND SECOND SECOND HYDROGENATIONHYDROGENATION HYDROGENATION DISTILLATION DISTILLATION DISTILLATIONBolloms Bottoms Bofloms Thermally Stable Thermally Stable ThermallySloble Je'r Fuel Jel fuel Jet l'-'uel I L. 4.. l l Thermally Stable JetFuel INVENTORS:

Marv/n J. Denherder BY Wilford J. Zimmersc/zied WM/QM A TTOR/VE Y 1966M. J. DEN HERDER ET AL 3,236,764

JET FUEL MANUFACTURE 2 Sheets-Sheet 2 Original Filed June 29, 1961HEddlHlS HHddlHiS ATTORNEY United States Patent 3,236,764 JET FUELMANUFACTURE Marvin I. Den Herder, Olympia Fields, 101., and Wilford J.Zimmerschied, Crown Point, Ind., assignors to Standard Uil Company,Chicago, 11]., a corporation of lndiana Continuation of application Ser.No. 120,542, June 29, 1961. This application Nov. 27, 1964, Ser. No.414,355

4 Claims. (Cl. 208210) This is a continuation of co-pending applicationSerial No. 120,542, filed June 29, 1961, now abandoned, whichapplication is in turn a continuation-in-part of application Serial No.804,437, filed April 6, 1959, now US. Patent 3,126,330.

This invention relates to the production of a high performance jet fuelof the type required by supersonic aircraft or ballistic missiles, whichfuel is characterized by high temperature stability, maximum energycontent, and good handling characteristics at both high and lowtemperatures. The invention particularly relates to the manufacture ofsuch a jet fuel from cycle gas oil, i.e., the refractory gas oilseparated from product gasoline produced by catalytically cracking gasoil, by a coordinated sequence of distillations and hydrogenations ofselective fractions from such oil.

Fuels for supersonic jet engines should have net heats of combustionupwards from about 18,400 B.t.u. per pound and 130,000 B.t.u. pergallon, an aromatics content of as low as possible, a freezing pointbelow 40 F., good stability at high temperatures, and low viscosity at-30 F. Stability at high temperatures, in the region of about 800 F., isnecessary in order to permit use of the fuel prior to combustion thereofas a coolant for the engine and air frame. The object of this inventionis to provide a high performance jet fuel which will meet theserequirements, and to do so by a technique which will not requireexcessive capital investment and operating expense. Additionally, thisinvention enables the manufacture of such a jet fuel from raw material(cycle gas oil, hereinafter referred to as cat gas oil) which isavailable in large supply in most refineries. This invention contributesto the defense of the nation by enabling the production of greaterquantities of high performance jet fuel as a result of utilizing a rawmaterial which is plentifully available, than has been heretoforepossible.

The thermally stable jet fuel of this invention comprises condensedbicyclic naphthenes (generally called decalins) substantially free ofaromatics and parafiins. Decalins are present in crude petroleum, butcomprise usually only a small fraction of crude petroleum and are notreadily separated from other hydrocarbons of comparable boiling rangewhich occur in crude oil. A similar situation exists in respect of thecorresponding condensed bicyclic aromatics (usually callednaphthalenes). However, condensed bicyclic aromatics having less than 15carbon atoms per molecule are present in cat gas oil in a significantlygreater concentration than in that portion of crude oil corresponding inboiling range to the cat gas oil. However, even with the increasedconcentration of the condensed bicyclic aromatics, the cat gas oilcontains large amounts of paraffins and monocyclic naphthenes andaromatics which boil in the same range as the above referred tocondensed bicyclic aromatics.

This invention is directed to the manufacture of a thermally stable jetfuel comprising decalins substantially free of aromatics and paraffiusfrom selected narrow boiling fractions of cat gas oil. As illustrated inFIGURE 1, catalytically cracked gas oil-is fractionated into narrowfractions each boiling within a 60 F. boiling range, preferably intofractions of 30-40 boiling range, and which also boil within the rangeof about 450 to 570 F. The

narrow boiling fractions of cat gas oil are then subjected individuallyto a first hydrogenation in the presence of hydrogen and a sulfurresistant hydrogenation catalyst under hydrogenation conditionseffective to convert sulfur-containing and nitrogen-containing compoundsin such fractions to compounds boiling below the boiling range of suchfractions, and further effective to convert a substantial proportion ofthe condensed bicyclic aromatics in such fractions to tetralins. Thelower boiling sulfurand nitrogen-containing compounds and excesshydrogen are separated from the effluent from the first hydrogenation.The remainder of the first hydrogenation effluent is then subjected to asecond hydrogenation in the presence of hydrogen and a secondhydrogenation catalyst which is more active for hydrogenation ofhydrocarbons than the above-mentioned sulfur resistant catalyst underhydrogenation conditions effective to convert condensed bicyclichydrocarbons to decalins. The product, a thermally stable jet fuel, isthen separated from the effluent from the second hydrogenation bydistillation. The product jet fuel comprises decalins substantially freeof aromatics and paratfins and having heats of combustion of at least18,400 B.t.u. per pound and 131,000 B.t.u. per gallon, and a freezingpoint of not greater than about -70 F.

The cat gas oil used as raw material for this process may be obtainedfrom any of the conventional catalytic cracking processes, either fixedbed, moving bed, or fluidized bed. The source of the feed to thecatalytic cracking unit is unimportant. The severity of the catalyticcracking operation does influence the desirability of the resulting catgas oil for use in this process, in that a high severity catalyticcracking operation yields cat gas oil having a higher percentage ofcondensed bicyclic aromatics than does low severity operations. However,this is merely a question of desirability; a cat gas oil from a lowseverity catalytic cracking operation is suitable for use in thisprocess, although it will yield a smaller percentage of product jetfuel.

The cat gas oil is distilled into one or more fractions boiling within a60 F. boiling range, preferably a boiling range of 3040 F., and whichfractions also boil individually within the range of about 450 to 570 F.A large number of the alkyl naphthalenes having 11 to 14 .carbon atomsper molecule boil within such range. Conventional distillation equipmentmay be used, but should be designed to give sufficiently sharpfractionation to minimize the boiling range over-lap between successivenarrow boiling fractions of cat gas oil taken from the distillationtower for processing in this invention.

The first hydrogenation of a narrow boiling cat gas oil fraction isconducted in the presence of hydrogen and a sulfur resistanthydrogenation catalyst. This first hydrogenation is conducted atconditions effective to desulfurize and denitrogenize the narrow boilingfraction, and also effective to convert a substantial proportion of thecondensed bicyclic aromatics to tetralin. Illustrative sulfur resistantcatalysts are those comprising cobaltmolybdenum, generally supported onalumina, nickel sulfide and nickel-tungsten sulfide. The catalyst may beused in any of several different physical forms, such as granules, orshaped into pellets or pills, and the like, when a fixed catalyst bedhydrogenation unit is used, or even as a fiuidizable powder if a fluidbed system is to be used. Because of the high pressure involved, thehydrogenations of this invention are preferably conducted in fixed bedunits.

The primary criteria of the hydrogenation conditions to be used are thatthe narrow boiling cat gas oil fraction be substantially desulfurizedand denitrogenized, and that a substantial proportion, advantageouslymore than half, of the condensed bicyclic aromatics be converted totetralin. It is desirable to minimize cracking of the hydrogenationfeed, and to this end the hydrogenation temperature should notsubstantially exceed 800 F., and is preferably in the range of 675800F., advantageously 720-750 F. The hydrogenation pressure may vary fromabout 400 p.s.i.g., to several thousand pounds p.s.i.g., preferably fromabout 1000 to 2500 p.s.i.g., and advantageously about 1500 p.s.i.g. Thetemperature and pressure of hydrogenation should be correlated, usingincreasing pressure as the temperature is increased. Liquid hourly spacevelocities in the range of 0.1 to may be used, preferably spacevelocities in the range of about 0.5 to 2.

The amount of hydrogen chemically consumed in the first hydrogenationdepends upon the extent to which condensed aromatics are hydrogenated,the fraction of the feed which comprises readily hydrogenatablecompounds, and, to a lesser extent, the amount of nitrogen and sulfur inthe feed. However, as an approximation it may be expected that about 30to 50 percent of the total hydrogen chemically consumed within theprocess will be consumed in the first hydrogenation. The theoreticalhydrogen consumption for converting methyl naphthalene to methyltetralin is about 1900 s.c.f. per barrel of methyl naphthalene; theconversion of the methyl tetralin to methyl decalin requires about anadditional 2800 s.c.f. per barrel of methyl naphthalene feed. Slightlylesser amounts of hydrogen are required for the hydrogenation of C and Cnaphthalenes to their corresponding decalins. In respect of anyparticular narrow boiling cat gas oil the hydrogen which will bechemically consumed may be already calculated from the knowledge of thecomposition of such fractions, including data on the sulfur and nitrogencontent thereof.

It is desirable to conduct the hydrogenation in the presence of excesshydrogen. Therefore, the amount of hydrogen charged to the firsthydrogenation unit may range from about 1500 s.c.f per barrel of liquidcharge to 10,000 s.c.f. per barrel, preferably 2500 to 6000 s.c.f. perbarrel. The hydrogen used does not need to be of any exceptional purity,and may be the hydrogen make-gas from a catalytic reforming operationwhich comprises about 75 mol percent hydrogen and the remainderprimarily light hydrocarbons.

The presence of H 8 in the hydrogen feed gas is not objectionable.

After the first hydrogenation, the etfiuent therefrom is cooled and thegaseous phase separated from the liquid phase. The gaseous phasecomprises predominantly hydrogen and includes light hydrocarbons,hydrogen sulfide, and in many instances ammonia. The gaseous phase ofthe efiluent may be rejected from the system and used for some otherpurpose, or it may be recycled to the first hydrogenation unit, or used,after removal of hydrogen sulfide and ammonia, in the hereinafterdescribed second hydrogenation step. If it is recycled to the firsthydrogenation unit, it is preferable to process the stream through ahydrogen sulfide removal unit, such as an ethanol amine desulfurizer, inorder to prevent the build-up of hydrogen sulfide. It may be desirable,depending upon the cat gas oil fraction which has been hydrogenated andthe conditions of hydrogenation, to strip dissolved contaminants fromthe liquid phase of the first hydrogenation effluent prior to againhydrogenating the liquid phase.

The hydrogenation of the above-mentioned liquid phase is conducted inthe presence of hydrogen and a catalyst which is more active forhydrogenation of hydrocarbons than the above-described sulfur resistantcatalyst under conditions which are effective to convert condensedbicyclic hydrocarbons to decalins. The greater hydrogenation activity ofthe catalyst used in the second hydrogenation is required because of thegreater difficulty in hydrogenating tetralins to decalins compared tothe hydrogenation of naphthalenes to tetralins. Suitable catalysts foruse in the second hydrogenation include supported 7 nickel, e.g.,nick-el onralumina or kieselguhr, or a noble metal such as platinum orpalladium, on alumina. It is preferred that the catalyst have a minimumof cracking activity, and for that reason it is desirable that thecatalyst be substantially free of halides. Relatively lower temperaturesare used in the second hydrogenation unit than in the firsthydrogenation unit, also in order to minimize cracking. Temperatures inthe range of 575 to 700, preferably 600 to 650 F. are used. Thepressures described above in respect to the first hydrogenation unit aresuitable for use in the second unit, and it is frequently desirable touse comparable pressures in each unit, Liquid hourly space velocities inthe range of 0.1 to about 5, preferably from A to about A may be used.Generally, a lower space velocity will be used in the secondhydrogenation unit than in the first hydrogenation unit. The amount ofhydrogen charged to the unit will be in the general range as disclosedabove in respect of the first hydrogenation unit, but will generally besomewhat higher, in any given plant practicing this invention, in thesecond hydrogenation unit. Inasmuch as the catalyst suitable for use inthe second hydrogenation unit are not only more active but are also lesssulfur resistant than the catalysts which may be used in the firsthydrogenation unit, the hydrogen charged to the second unit should besubstantially free of hydrogen sulfide.

The efiluent from the second hydrogenation unit is separated into agaseous phase and a liquid phase. The gaseous phase comprisespredominantly hydrogen having a low sulfur content and is advantageouslyrecycled within the system. The liquid phase is distilled to obtain theproduct fuel. It is frequently advantageous, although not mandatory, toremove the lowest boiling 1-10 percent of the liquid phase as a forecut,and withdrawing the product jet fuel as a side stream heart cut from thedistillation tower. Depending upon the cat gas oil and variousparticulars of the processing sequence, the product jet fuel will amountto A to about /2 or more of the liquid phase charged to the finaldistillation. The above-mentioned forecut, if taken, comprises asubstantially saturated hydrocarbon stream suitable for use in kerosene.The bottom stream from the distillation is also substantially saturated,will generally have a high cetane number, and is advantageously blendedinto diesel fuel.

The following information will delineate this invention with greaterspecificity. Light cat gas oil obtained from a fluid catalytic crackingunit was distilled into three narrow boiling cat gas oil fractions.Inspection test data on the distillation charge and on the narrowboiling fractions distilled therefrom are given in Table I:

Cat gas oil fraction No. 1 was first hydrogenated over acobalt-molybdenum catalyst supported on alumina at 730740 F., a pressureof 1500 p.s.i.g., and a volume hourly space velocity of 1.0. Bottledhydrogen, in a nonrecycle system, was used in the amount of 3100 s.c.f.of. hydrogen per barrel of cat oil fraction No. l. The effluent from thehydrogenation was cooled and separated into gaseous and liquid products.The liquid product was then rehydrogenated over a catalyst comprising 1weight percent platinum-on-alumina which was substantially free ofhalide. This hydrogenation was conducted at 630 F., a pressure of 1500p.s.i.g., and a volume hourly space velocity of 0.5. As before,once-through hydrogen was used in the amount of 4000 s.c.f. per barrelof liquid feed to the hydrogenation. Both hydrogenation steps wereconducted in bench scale isothermal reactors. Inspection tests on theeffluent from each hydrogenation step referred to above are given inTable II. It is noted that the first hydrogenation reduced the sulfurcontent from 0.64 weight percent to 0.001 percent.

Table II.Processing of cat gas oil fraction N0. 1

The liquid product from the second hydrogenation was distilled into aplurality of small cuts, and each cut analyzed for heat content,specific gravity, and freezing point. For the cuts which represented the2 volume percent through 46 volume percent of the liquid efliuent fromthe second hydrogenation, the heats of combustion varied from 18,490 to18,562 B.t.u. per pound, and from 131,029 to 132,045 B.t.u. per gallon.The weighted average heat contents were 18,520 B.t.u. per pound and131,667 B.t.u. per gallon. The freezing points of the various cuts wereall below 80 F., and the aromatic contents were less than 2.5 volumepercent.

Cat gas oil fractions 2 and 3, as referred to in Table I above, wereprocessed in a similar manner using the same process conditions and typeof catalyst. Data on the liquid phase of the effluent from eachhydrogenation step is set forth in Tables III and IV.

Table III.Prcessing of cat gas oil fraction N0. 2

First Second Hydrogena- Hydrogenation Efiiluent tion Efiiuent Gravity,API 34.5 37. 6 ASTM Distillation:

iti 421 430 10% 458 457 30%. 485 476 50%. 496 490 70% 507 504 90% 519519 Max 531 520 Sulfur, wt. percent 0.002 0. 001 Yield, vol. percent ofFraction 104. 106. 5

Table IV.-Pr0cessing of cat gas oil fraction N0. 3

In respect of cat gas oil fraction No. 2, the heats of combustiondetermined on fractions representing 12 through 52 volume percent of thefinal liquid hydrogenation product varied between the limits of 18,263to 18,560 B.t.u. per pound, and from 131,667 through 133,831 B.t.u. per

gallon. The weighted average heat contents were 18,450 B.t.u. per poundand 132,590 B.t.u. per gallon. The average aromatics content was between2.0 and 2.5 volume percent.

In respect of cat gas oil fraction No. 3, the fractions representingfrom 8.8 through 31.8 volume percent of the final liquid hydrogenationproduct had weighted average heats of combustion of 18,457 B.t.u. perpound and 135,644 B.t.u. per gallon. The composite freezing point wasabout F.; the aromatics content was between 1.5 and 2 percent.

The product jet fuel comprises predominantly decalins substantially freeof paraffins and aromatics. In addition to its use as a jet fuel, theproduct of this process may also be used as a raw material foradditional chemical processes. In this connection it is to be understoodthat as used herein the word decalins includes not only the fullysaturated molecule (Ciel I18) resulting from the hydrogenation ofnaphthalene, but also alkyl substituted homologues thereof. Furthermore,the product fuel may and often will contain minor proportions, amountingto a few percentage points, of fully saturated derivatives of decalinwherein an alkyl substituent has formed a bridge between the twosaturated 6-carbon atom rings, e.g., the fully saturated compoundresulting from the hydrogenation of acenaphthylene.

The invention will be more clearly understood from the followingdetailed description of a specific example read in conjunction withaccompanying FIGURE 2 which forms a part of the specification, and whichis a schematic flow diagram illustrating the process of the invention.

A catalytic gas oil from a catalytic cracking unit is introduced throughline 11 to distillation column 12. The charge to the distillation columnmay be heated by a heater, not shown. From the distillation column 12are withdrawn one or more cat gas oil fractions designatcd fractions 1,2 and 3 through lines 13a, 13b and 130, which are collected in storagetanks 14a, 14b and 140. The distillation is conducted so that thesefractions have a narrow boiling range of not more than about 60 F.,preferably 30-40 F., and in addition each boils within the range ofabout 450-570 F. Collecting these fractions in tankage is not essential,but is a convenient expedient where only one set of hydrogenationreactors is available for subsequent processing on a blocked-out basis.Depending upon the boiling range of the cat gas oil charge, an over-headcut may be optionally taken through line 15 and disposed of outside ofthe system, for instance, by blending into a No. 2 furnace oil. Insimilar fashion, it is generally advantageous to take a bottoms cutthrough line 16 for blending into No. 2 furnace oil.

The description of FIGURE 2 continues with respect to fraction No. 2stored tank 14b. However, it is to be understood that the processingsequence described with respect thereto is applicable on a blocked-outbasis to fractions 1 and 3. It is also to be understood that the figureomits graphic representation of heaters, heat exchangers, pumps,compressors and valves, which are believed to be unnecessary to anacceptable understanding of the process.

The cat gas oil fraction is withdrawn from tank 1412 through line 17,and heated to an elevated temperature which, because of the exothermiccharacter of the hydrogenation reaction, will generally be somewhatbelow the intended operating temperature of 675800 F. Hydrogen fromlines 18 and 19 is mixed with the cat gas oil fraction prior to thecharging thereof to the first hydrogenation unit 20. The hydrogenationunit 20 is operated at pressures, space velocities, and hydrogen chargerates as hereinabove described. The hydrogenation unit uses a sulfurresistant catalyst, such a cobalt-molybdate on alumina, preferably inthe form of a fixed bed. Hydrogenation unit 20 may comprise one or morereactors in parallel which are, because of the high exothermic nature ofthe hydrogenation reaction, provided with suitable heat removal means,such as a molten salt or a eutectic mixture comprising biphenyl(generally referred to as Dowtherm) circulated through internal tubes.

The effluent from hydrogenation unit is withdrawn through line 21,cooled and run to separator 22, wherein a hydrogen-rich gas phase isseparated from liquid hydrocarbons. The hydrogen-rich gas phase willhave a lower hydrogen concentration than the hydrogen introduced throughline 19, because of both hydrogen consumed and also because of dilutionwith a minor amount of light hydrocarbons cracked during thehydrogenation process. It will also contain increased amounts ofhydrogen sulfide and ammonia as a result of the removal of sulfur andnitrogen from the cat gas oil fraction charged to the hydrogenationunit. The hydrogen-rich gas phase is withdrawn from the separator 22through line 23 and may be either rejected from the system through line24 or recycled via line 25 to the hydrogenation unit. If the latterprocedure is followed, it is advantageous to process the hydrogen-richrecycle gas through a hydrogen sulfide removal unit 26, which may be ofa conventional type, e.g., an ethanol amine type of desulfurizer.Provision may also be made to reject from the system light hydrocarbonswhich may otherwise build up to undesirable concentrations.Hydrogen-rich recycle gas from hydrogen sulfide removal unit 26 isrecycled through lines 27, 28 and 19 to first hydrogenation unit 20.Provision may also be made for recycling hydrogen through line 29 to asecond hydrogenation unit described hereinafter.

From separator 22 the liquid phase effluent is withdrawn through line 30for further processing. This may optionally include, as shown in thefigure, stripping of the liquid phase in stripper 31 to complete theremoval of low boiling constitiuents, including ammonia and hydrogensulfide and light hydrocarbon gases, which are rejected through line 32as off-gas.

From stripper 31, liquid hydrocarbons are withdrawn through line 33,heated and mixed with hydrogen from line 34 prior to being chargedthrough line 35 to second hydrogenation unit 36. The hydrogen from line34 may be derived from an independent source through line 37, or it mayinclude hydrogen recycled through line 29 after having been purified inhydrogen sulfide removal unit 26, and may include recycle hydrogenseparated from the effluent from second hydrogenation unit 36.

Second hydrogenation unit 36 is operated at process conditions ashereinabove described, for instance, 650 F., 1500 p.s.i.g. pressure, /2volume hourly space velocity, and 4000 s.c.f. hydrogen per barrel ofliquid feed. The catalyst used is more active than the catalyst used infirst hydrogenation unit 20, and is suitable halide-free platinum onalumina. The catalyst and the process conditions used in conjunctiontherewith employed in second hydrogenation unit 36 are selected tocomplete the partial hydrogenation which was accomplished in firsthydrogenation unit 20. As was described in respect of firsthydrogenation unit 20, second hydrogenation unit 36 should be providedwith means to remove the exothermic heat of reaction resulting from thehydrogenation.

The efiiuent from second hydrogenation unit 36 is removed through line36a, cooled, and separated into gaseous and liquid phases in separator38. The hydrogenrich gaseous phase is removed through line 38a andeither rejected from the system through line 39 or, more preferably, andwith provision for avoiding the build-up in concentration of lighthydrocarbons therein, recycled through line 40 to hydrogenation unit 36.The liquid phase is withdrawn from separator 38 through line 41 andcharged to distillation tower 42. From tower 42 a light ends forecut maybe optionally taken over-head through line 43 for blending into asuitable product, such as kerosene. The jet fuel which is the product ofthis process is withdrawn through line 44, and a bottom cut suitable foruse, for instance, in diesel fuel, is withdrawn through line 45. Theproduct jet fuel withdrawn through line 44 comprises predominantlydecalins substantially free of aromatics and paraffins and having heatof combustion of at least about 18,400 B.t.u. per pound and about131,000 B.t.u. per gallon, and a freezing point of not greater thanabout 70 F. The viscosities at 30 F. of the jet fuels produced by thisprocess are in the range of about 15-50 centistokes.

The heats of combustion referred to above were calculated from hydrogencontent (Industrial and Engineering Chemistry, volume 43, page 94 1)which in turn was obtained in the manner described in AnalyticalChemistry, volume 23, page 324. The freezing point data were determinedby ASTM designation Dl477-57T. The quantities of naphthalene andtetralins were determined by the fluorescent indicator analysesprescribed by ASTM designation method D-1319.

Having thus described the invention, what is claimed 1. A process formanufacturing thermally stable jet fuel, which process comprisesseparating by distillation from catalytically cracked gas oil containingcondensed bicyclic hydrocarbons a plurality of fractions each boilingwithin a 60 F. boiling range and also each boiling within the range ofabout 450 to 570 F., subjecting each of said farctions to a firsthydrogenation in the presence of hydrogen and a sulfur-resistanthydrogenation catalyst under hydrogenation conditions including atemperature in the range of about 675 to 800 F., a pressure in the rangeof about 400 to 2500 p.s.i.g. and a liquid-hourly space velocity in therange of about 0.1 to 10, effective to convert sulfur-containing andnitrogen-containing compounds in each of said fractions to sulfurandnitrogencontaining compounds boiling below said fractions and effectiveto convert a substantial proportion of the condensed bicyclic aromaticsin each of said fractions to tetralins, separating from the efiluentfrom each of said first hydrogenations sulfurand nitrogen-containingcompounds boiling below said fractions and hydrogen, thereaftersubjecting the remainder of said hydrogenation efiluents to a secondhydrogenation in the presence of hydrogen and a second hydrogenationcatalyst which is more active for hydrogenation of hydrocarbons thansaid sulfurresistant catalyst under conditions including a temperaturein the range of about 575 to 700 -F., a pressure in the range of about400 to 2500 p.s.i.g. and a liquid hourly space velocity in the range ofabout 0.1 to 5, effective to convert condensed bicyclic hydrocarbons todecalins and separating by distillation from the efiluent of each ofsaid second hydrogenations a thermally stable jet fuel comprisingdecalins substantially free of aromatics and paraffins, said jet fuelhaving a heat of combustion of at least about 18,400 B.t.u. per pound,and about 131,000 B.t.u. per gallon, and a freezing point of not greaterthan about 70 F.

2. The process of claim 1 wherein said sulfur-resistant catalystcomprises supported cobalt molybdenum, and where said secondhydrogenation catalyst comprises platinum-on-alumina.

3. The process of claim 1 wherein said second hydrogenation catalystcomprises metallic nickel.

4. The method of making thermally stable, highly naphthenic condensedbicyclic hydrocarbon jet fuel of high heat content and low freezingpoint and substantially free of aromatics and paraffins, which methodcomprises separately hydrofining each of a plurality of cycle gas oilfractions each containing condensed bicyclic hydrocarbons underconditions including a temperature in the range of about 675 to 800 F.,a pressure in the range of about 400 to 2500 p.s.i.g. and aliquid-hourly space velocity in the range of about 0.1 to 10 foreffecting desulfurization thereof and converting a substantialproportion of condensed bicyclic aromatics in each of said gas oilfractions to tetralins, said fractions each boiling within a 60 F.boiling range and also within the 9 limits of about 450 to 570 F.,saturating each of said hydrofined gas oil fractions by hydrogenation inthe presence of an active hydrogenation catalyst under conditionsincluding a temperature in the range of about 575 to 700 F., a pressurein the range of about 400 to 5 2500 p.s.i.g. and a liquid hourly spacevelocity in the range of about 0.1 to 5, and distilling each of theresulting hydrogenation products to obtain as said jet fuel highlynaphthenic fractions each boiling below the boiling range of therespective fraction fed to said hydrofining and comprising predominantlycondensed bicyclic hydrocarbons substantially free from parafiins andaromatics.

References Cited by the Examiner UNITED STATES PATENTS 2,671,754 3/1954De Rosset et a1. 208-89 2,878,179 3/1959 Hennig 20857 2,956,002 10/1960Folkins 208-15 DELBERT E. GANTZ, Primary Examiner.

ALPHONSO D. SULLIVAN, Examiner.

1. A PROCESS FOR MANUFACTURING THERMALLY STABLE JET FUEL, WHICH PROCESSCOMPRISES SEPARATING BY DISTILLATION FROM CATALYTICALLY CRACKED GAS OILCONTAINING CONDENSED BICYCLIC HYDROCARBONS A PLURALITY OF FRACTIONS EACHBOILING WITHIN A 60*F. BOILING RANGE AND ALSO EACH BOILING WITHIN THERANGE OF ABOUT 450 TO 570*F., SUBJECTING EACH OF SAID FRACTIONS TO AFIRST HYDROGENATION IN THE PRESENCE OF HYDROGEN AND A SULFUR-RESISTANTHYDROGENATION CATALYST UNDER HYDROGENATION CONDITIONS INCLUDING ATEMPERATURE IN THE RANGE OF ABOUT 675 TO 800*F., A PRESSURE IN THE RANGEOF ABOUT 400 TO 2500 P.S.I.G. AND A LIQUID-HOURLY SPACE VELOCITY IN THERANGE OF ABOUT 0.1 TO 10, EFFECTIVE TO CONVERT SULFUR-CONTAINING ANDNITROGEN-CONTAINING COMPOUNDS IN EACH OF SAID FRACTIONS TO SULFUR- ANDNITROGENCONTAINING COMPOUNDS BOILING BELOW SAID FRACTIONS AND EFFECTIVETO CONVERT A SUBSTANTIAL PROPORTION OF THE CONDENSED BICYCLIC AROMATICSIN EACH OF SAID FRACTIONS TO TETRALINS, SEPARATING FROM THE EFFLUENTFROM EACH OF SAID FIRST HYDROGENATIONS SULFUR- AND INTROGEN-CONTAININGCOMPOUNDS BOILING BELOW SAID FRACTIONS AND HYDROGEN, THEREAFTERSUBJECTING THE REMAINDER OF SAID HYDROGENATION EFFLUENTS TO A SECONDHYDROGENATION IN THE PRESENCE OF HYDROGEN AND A SECOND HYDROGENATIONCATALYST WHICH IS MORE ACTIVE FOR HYDROGENATION OF HYDROCARBONS THANSAID SULFURRESISTANT CATALYST UNDER CONDITIONS INCLUDING A TEMPERATUREIN THE RANGE OF ABOUT 575 TO 700*F., A PRESSURE IN THE RANGE OF ABOUT400 TO 2500 P.S.I.G. AND A LIQUID HOURLY SPACE VELOCITY IN THE RANGE OFABOUT 0.1 TO 5, EFFECTIVE TO CONVERT CONDENSED BICYCLIC HYDROCARBONS TODECALINS AND SEPARATING BY DISTILLATION FROM THE EFFLUENT OF EACH OFSAID SECOND HYDROGENATIONS A THERMALLY STABLE JET FUEL COMPRISINGDECALINS SUBSTANTIALLY FREE OF AROMATICS AND PARAFFINS, SAID JET FUELHAVING A HEAT OF COMBUSTION OF AT LEAST ABOUT 18,400 B.T.U. PER POUND,AND ABOUT 131,000 B.T.U. PER GALLON, AND A FREEZING POINT OF NOT GREATERTHAN ABOUT -70*F.